I purchased a Carrier Performance 15 SEER unit in June based on Carrier reliability, SEER rating, and low noise level. I have noticed a loud slamming noise when the compressor shuts off and have had two techs take a look and they both say the noise is normal. I find it hard to believe that Carrier would claim that this unit is ultra quiet when it makes such a loud "normal" noise. Has anyone experienced this noise and is it normal? If so, how could Carrier claimer this is an ultra quiet unit? My neighbor installed an American Standard unit at the same time and I'm thinking I made a huge, costly mistake by going with the Carrier unit, as I can not hear his when it is running or when it shuts off.